Garnet Electrolyte with an Ultralow Interfacial Resistance for Li-Metal Batteries

• Published in: Journal of the American Chemical Society Vol. 140; no. 20; pp. 6448 - 6455
• Main Authors: Li, Yutao, Chen, Xi, Dolocan, Andrei, Cui, Zhiming, Xin, Sen, Xue, Leigang, Xu, Henghui, Park, Kyusung, Goodenough, John B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 23.05.2018; American Chemical Society (ACS)
• Subjects: Chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.8b03106

Garnet-structured Li7La3Zr2O12 is a promising solid Li-ion electrolyte for all-solid-state Li-metal batteries and Li-redox-flow batteries owing to its high Li-ion conductivity at room temperature and good electrochemical stability with Li metal. However, there are still three major challenges unsolved: (1) the controversial electrochemical window of garnet, (2) the impractically large resistance at a garnet/electrode interface and the fast lithium-dendrite growth along the grain boundaries of the garnet pellet, and (3) the fast degradation during storage. We have found that these challenges are closely related to a thick Li2CO3 layer and the Li–Al–O glass phase on the surface of garnet materials. Here we introduce a simple method to remove Li2CO3 and the protons in the garnet framework by reacting garnet with carbon at 700 °C; moreover, the amount of the Li–Al–O glass phase with a low Li-ion conductivity in the grain boundary on the garnet surface was also reduced. The surface of the carbon-treated garnet pellets is free of Li2CO3 and is wet by a metallic lithium anode, an organic electrolyte, and a solid composite cathode. The carbon post-treatment has reduced significantly the interfacial resistances to 28, 92 (at 65 °C), and 45 Ω cm2 at Li/garnet, garnet/LiFePO4, and garnet/organic-liquid interfaces, respectively. A symmetric Li/garnet/Li, an all-solid-state Li/garnet/LiFePO4, and a hybrid Li–S cell show small overpotentials, high Coulombic efficiencies, and stable cycling performance.